1. Field of the Invention
The invention relates to a technical field of ad-hoc networks and, more particularly, to a channel assigning method for supporting real-time traffic in an ad-hoc network.
2. Description of Related Art
Currently, mobile ad-hoc network is one of the well-developed wireless networks. In fact, mobile ad-hoc networks consist of distributed mobile nodes that communicate with one another. As compared to other networks such as mobile phone networks or satellite networks, ad-hoc networks are characterized in having no fixed infrastructure but mobile nodes only. With the capability of transmission in a limited area, a node can be a relay to forward its neighbors' data. Accordingly, a network is generated by communication among the mobile nodes and its topology is changed dynamically when mobile nodes leave or join the network. Thus, ad-hoc networks have relative flexibility and robustness for strict environments without using a fixed infrastructure. For example, an ad-hoc network can be deployed rapidly in a battlefield or a natural disaster area subjected by, such as an earthquake, thereby providing required communication services.
In the cited ad-hoc networks, an effective communication distance between two mobile nodes is referred to as a hop. Because effective communication distance of each mobile node is limited, when two mobile nodes have a distance greater than the effective communication distance and intent to establish a communication connection, other mobile nodes between the two mobile nodes are used as relays to forward data, which forms a multi-hop environment. A typical wireless network such as a mobile phone network can easily realize bandwidth reservation because its infrastructure allows all communication requirements of mobile phones to be obtained by corresponding base stations. However, an ad-hoc network has complicated scheduling for obtained channels because of no collective resource control and allocation mechanism. Further, the ad-hoc network is operated in an open wireless communication platform that can incur interference. Accordingly, it is not easy to carry out QoS guarantee to support real-time traffic as establishing required connection and bandwidth reservation in a multi-hop network. The ad-hoc network has to apply distributed computation for obtaining required control function. In this case, the distributed computation needs to arrange the ad-hoc network into a hierarchical configuration. Therefore, a clustered ad-hoc network configured by grouping mobile nodes is widely used. As shown in FIG. 1, each cluster 11 typically consists of nearby mobile nodes 12. Mobile nodes 12 in a same cluster 11 can communicate with one another and one of two adjacent clusters 11 has at least one mobile node 12 as a gateway node to communicate with the other cluster 11.
Time division multiple access (TDMA) technique is applied to common wireless channels among mobile nodes 12 in the ad-hoc network for bandwidth allocation. Namely, a channel substantially has a time slot and a code. When a link is established, a transmitting node 121 and a receiving node 123 communicate with each other using a same code in an allocated time slot, thereby transmitting and receiving packets. A challenge of such an ad-hoc network is in that how channels are allocated appropriately among the clusters 11 to ensure data transmission success without collision, and also channel utilization rate is increased to enhance system performance.
A code is assigned to a match with respect to a mobile node 12, for arranging a common channel. If the number of available codes is greater than the number of mobile nodes 12, every mobile node 12 can have an assignment code. In this case, communication is achieved by two ways: receiver-based code assignment (RCA) that a transmitting terminal communicates with a receiving terminal based on a code of the receiving terminal; and transmitter-based code assignment (TCA) that a receiving terminal receives data from a transmitting terminal based on a code of the transmitting terminal. However, in typically ad-hoc networks, the number of available codes is usually smaller than the number of mobile nodes 12, and thus to use the codes repeatedly and effectively becomes an important subject.
In addition, as shown in FIG. 1, in the ad-hoc network, two nodes 121 and 122 having an ineffective communication distance from each other may send packets to a node 123 concurrently, which thus causes a head-on collision, or the node 121 sends a packet to the node 124 and the node 122 sends a packet to the node 123, which causes a side-way collision. Thus, a hidden terminal problem is encountered which needs to be overcome in system design.